Ecologie benthique de la Lagune Ebrié. Détermination du rapport de stabilité biocoenotique (RSB)

The 1912 Jaccard index modification led to the formulation of the Biocoenotic Stability Report (BSR). It is another similarity index based on the evaluation of two opposite ecological states affecting both compared biotopes.

Ecologie benthique de la Lagune Ebrié. Théorie sur la méthode du DR' pour la mise en évidence de biocoenoses

The theoretical aspect of the DR' method was presented. It suggestes the association of some characteristic transects, the organisms of which will be used to describe the first biocoenoses of the Ebrié lagoon.

Contribution à l'étude des modifications hydro-sédimentaires consécutives à la réouverture artificielle de l'embouchure du Comoé à Grand-Bassam

The Bassam artificial inlet was opened (in September 22, 1987) in order to revacuate offshore invasive aquatic plants. This has considerably modified the hydro-sedimentary environment of the lagoonal domain at Grand-Bassam. Tidal currents effect has confered the lagoonal waters an estuarine feature, the saline intrusion (25-35%o) increased beyond the Moossou bridges up to the confluence of the Comoe river. This has led to a cleaning of the river lower course and above all to the bottoms of the lagoon, which were previously confined. The remobilization of mud (from lagoonal bottoms around Bouet Island) evacuated offshore, has exposed lagoonal and oceanic sandy features. This new system remains fragile, with the seasonal (low river-flow) clogging.

Les effets de la réouverture de l'embouchure du fleuve Comoé sur le végétation littorale lagunaire (Lagune Ebrié - Côte d'Ivoire)

The results of floristic data collected during two surveys in the eastern region of Ebrié lagoon in 1987 (before the reopening of the inlet) and in 1988 (after the reopening of the inlet) are discussed in this article. Salinity increase (from 4‰ to 30‰) as a result of the reopening in September 1987 of the channel of Comoé river, profoundly modified qualitatively and quantitatively, the plant population. Floating or fixed macrophytes have been completely destroyed. Mangrove forest being the hydrophytic belt of the lagunar rives.

Analyse des effets de l'ouverture du chenal de Grand Bassam (estuaire du fleuve Comoé, Lagune Ebrié) sur la macrofaune benthique lagunaire

This paper presents the results of a comparative study of three series of samples collected in the area near the Bassam channel before, six and twenty months after its opening in September 1987. Observed effects are the decrease in the abundance and the modification of the benthic macrofauna composition. These effects appeared to be definitive, without recovery of the most abundant species Corbula trigona. Most differences noted in the population structure are due to the increase of the salinity and at a least degree to the modification of the nature of the sediment.

Influence de la réouverture du canal de Bassam sur la pêcherie de crabes de Vitré II en Lagune Ebrié (Côte d'Ivoire)

This work is the result of one year of investigation from May 1987 to June 1988 among fishermen of Vitré II village located in the eastern region of the Ebrié lagoon.

Phytotoxicité du glyphosate sur la Jacinthe d'eau (Eichhornia crassipes, Solms)

The toxicity of the herbicide glyphosate was tested on water hyacinth (Eichhornia crassipes) samples cultivated in glass aquariums. The lowest dose (0.09 g.m-2) leads to an increasing plant growth rate. This growth rate decreases with intermediate doses (0.18 and 0.36 g.m-2), the consequence of which is to increase stolons (vegetative reproduction). On the other hand, the dose of 0.72 g.m-2 leads to a total and irreversible destruction of plants.

Étude comparative de la macrofaune associée aux racines de Pistia stratiotes L. (Araceae) du lac de barrage d'Ayamé II et du fleuve Comoé (Côte d'Ivoire)

Abundance and species variations of the macrofauna associated with the roots of Pistia stratiotes of Ayamé II lake and Comoé river were studied during one year. Samples of plants were collected by hand once a month within a sampler of 1 m2 of surface.

Variations saisonnières des facteurs hydrologiques et du biovolume microalgal benthique au sein d'un habitat artificiel (acadja-enclos) dans la lagune Ebrié: site d'Adjapoté

This paper presents the results of a comparative study of chemical and physical characteristics (temperature, oxygen, salinity, turbidity, pH, nutrient: phosphates, nitrates, nitrites, ammoniac) within the extensive aquaculture structure (acadja-enclosure or artificial habitats for fishes) and in the surrounding water. Biological characteristics of the periphyton growing on bamboos from acadja-enclosure were also described.

Élevage du silure Heterobranchus longifilis Val. en bassins sans renouvellement d'eau: effets de l'évolution de quelques paramètres chimiques de l'eau sur la croissance et la survie

African catfish (Heterobranchus longifilis Valenciennes, 1840), with a mean weight of 37 g, were raised in 4 m3 concrete tanks, with or without water changes at densities of 10 and 20 fish per m3. The results indicate that, although the low water needs of this catfish offer hope for the productions of 150 tons/hectare/year, water quality must always be monitored.

La circulation superficielle dans la partie occidentale du Golfe de Guinée

Direct current measurements carried out for 10 years in the Gulf of Guinea clearly show the importance of transverse circulation. The general pattern of currents is characterized by an anticyclonic gyre. The seasonal variations of this circulation are calculated through the study of the 3-monthly averaged geostrophic currents. The biological consequences of such a circulation are outlined.

Note sur les biomasses pélagiques évaluées par écho-intégration dans la zone équatoriale du Golfe de Guinée: premiers résultats

An Echo-Integration survey on the equator made during he GARP Atlantic Tropical Experiment indicated an important biomass in the layer 0/100m. The changes of that biomass have been connected to hydrological conditions. Measurements of target strength have been made, and the biggest schools have been measured.

Estimations des potentiels de pêche des stocks démersaux ivoiriens par les modèles globaux. Effets de la prolifération du Baliste (Balistes capriscus)

Statistical data (1959-1977) of the trawling fishery off the continental shelf of Côte d'Ivoire has been fitted to the Fox (PRODFIT) global model. Owing to the proliferation of baliste (B. capriscus) since the years 1971-1972, data were divided into two groups. Maximum Sustainable Yield MSY: PMMC in the text), for the whole of commercial species in the continental shelf, decreased from 8800t to 5900t between the two periods; the difference represents balistes potentialities at bottom level. The model has also been fitted to data which concern Sciaenidae coastal community and Sparidae community which are parts by the 50 m isobathe. Deep layer (50-120m) MSY is at 2350t during the whole period of study. Until 1977, this potentiality was never reached, because of the low productivity of the Sparidae community.

Rélations hydrométéorologiques sur les côtes du Golfe de Guinée: influence de l'orientation de la côte

The Gulf of Guinea is remarkable for its abundant precipitations and negative anomalies of the surface water temperature. This originality comes from the southern monsoon which transfers the cold season to the middle of northern summer up to latitude 10 degrees North. Yearly precipitations, which can vary along the coast, are well in correlation with coast crossing air flow (r=0.71) and with the sea-air temperature difference (r=0.72). Precipitations provide a better correlation with surface temperatures (0.72) than with salinities (-0.63). The wind influence upon negative anomaly of the surface temperature is more clear on N-S coast (r=0.98) than on W-E coast (r=0.73) of the Gulf. Temporal correlations calculated on 16 years of observations in Pointe-Noire are in connection with previous spatial correlations. Coastal hydroclimates are thus likely to be deduced from meteorology.

Biologie de Penaeus duorarum notialis en Côte d'Ivoire. 4 - Rélations entre la répartition et les conditions du milieu. Étude des variations du sex-ratio

The analysis of the geographic and bathymetric distribution of Penaeus duorarum and, particularly P. d. notialis off Côte d'Ivoire and in its whole distribution area leads to the definition of the adult ecological requirements (temperature, salinity, grain size and sediment composition, organic matter) and the importance of the thermocline in the bathmetric distribution. The population structure study shows: (1) variations of size with depth, (2) variations of sex ratio, with size, depth and seasons.